During and after the First World War, President Woodrow Wilson developed an approach to international relations that challenged the dominant assumptions of Realism. Instead of a world order marked by alliances, arms races, and wars, Wilson offered a vision of a peaceful world and the rule of international law. While America ultimately rejected the League of Nations, the Wilsonian tradition has continued to exert a powerful influence on scholars and policymakers. This tutorial will intensively examine Wilson's efforts to recast the nature of the international system, the American rejection of his vision after the First World War, and the reshaping of Wilsonianism after the Second World War. We will spend equal time in the tutorial on both the theoretical and historical dimensions of Wilsonianism.